1. Field of the Invention
This invention relates to a device for controlling the transmission gear ratio of an infinitely variable transmission to a suitable gear ratio conforming to the running mode of a vehicle.
2. Description of the Prior Art
Electro-hydraulic servo systems using a spool valve type electro-hydraulic servo valve or a rotary servo valve have been popular as the conventional control device of infinitely variable transmissions. Such systems are costly because of the use of the servo valve, are complicated in structure, and have reliability problems caused by the influence of dust. Moreover, they suffer from other problems, including the problem that the speed control becomes unstable when electronic or mechanical abnormality occurs.